Many small parts are used in the assembly line production of manufactured products, such as cars and trucks. The small parts are, for example, fasteners, mechanical parts and other items used in the construction of vehicles and the like. These parts are supplied to assembly line operators at assembly work stations. An operator removes the parts from a supply container on a tray and assembles the parts on a moving flow of vehicles or vehicle sub-assemblies. It is essential that the parts container be positioned conveniently for ready access by the operator. When one container is empty, another container needs to be readily available. The tray on which the container is supported should be adjustable to accommodate the needs of each individual operator.